Contents of this Issue

Navigation

Page 25 of 64

A
D
V
A
N
C
E
D
M
A
T
E
R
I
A
L
S
&
P
R
O
C
E
S
S
E
S
|
J
U
N
E
2
0
1
5
2 3
STEEL REINFORCEMENT BAR:
A TENSILE TESTING GUIDE
Steel rebar is commonly used around the world to reinforce concrete.
Understanding the basics of rebar tensile testing is critical to ensuring
product quality.
Jef Shafer, Instron, Grove City, Pa.
S
teel reinforcing bar, or rebar, is em-
bedded in concrete to improve the
overall strength of the surrounding
concrete. Material product standards help
guarantee that rebar produced through-
out the world exhibits the same physical,
chemical, and mechanical properties re-
gardless of the source. Proper mechanical
testing is necessary to determine if the re-
bar meets its published specifications, en-
suring product quality. Mechanical test-
ing requirements for rebar can vary, but
typically fall into these main categories:
• Tensile
• Bend
• Compression
• Fatigue
Other related product testing, such
as slip testing of mechanical splices (cou-
plers), may also be required. This article
primarily focuses on the common—yet
sometimes challenging—tensile test.
TENSILE TESTING
AND STANDARDS
At the global level, technical com-
mittees governed by the International
Organization for Standardization (ISO)
develop product and testing standards
for reinforcement bar products. In ad-
dition to specifying properties such as
minimum upper yield strength (Reh),
Rm/Reh ratio, and elongation values
for ribbed steel bar products, ISO prod-
uct standards, such as ISO 6935-2, also
specify how to measure tensile proper-
ties. Unique testing requirements are
included directly in the standard and
additional reference is made to ISO
15630-1, which focuses specifically on
test methods for similar products. ISO
15630-1 provides further references to
the more general metals tensile testing
standard, ISO 6892-1, where applicable.
On a regional level, many countries
also have local standards organizations
that may have existed even before the
global ISO committees were formed.
They often maintain their own product
and testing standards or can elect to
adopt global ISO standards where ap-
propriate. For example, in the U.S., ASTM
has established product and testing
standards for rebar. Product standards
such as ASTM A615, A706, A955, and
A996, provide minimum product specifi-
cations and also include unique testing
details for determining tensile proper-
ties. Reference may also be made to ad-
ditional testing requirements found in
ASTM A370. This steel testing standard
covers mechanical testing of steel prod-
ucts. It then includes further reference
to the primary metals tensile testing
standard, ASTM E8.
Regardless of the governing body,
the information provided in most
global and local standards is quite de-
tailed and intended to help users un-
derstand the following basic testing
requirements:
• Required equipment
• Associated terminology and symbols
• Specimen preparation
TABLE 1—COMMON REBAR PRODUCT
AND TESTING STANDARDS
ISO ASTM
Rebar product
standard
6935-2 A615
Rebar testing
standard
15630-1 A370
Metals tensile
test standard
6892-1 E8
Uncoiled rebar with slight bends over length.